1. Field of the Invention
The present invention relates to a camera system including an image sensor having a focus detection pixel and a method for correcting the focus detection pixel.
2. Description of the Related Art
Imaging apparatuses that detect a focus state by using part of pixels of an image sensor as a focus detection element are known. The imaging apparatuses detect the focus state of an imaging lens by setting part of pixels of the image sensor as focus detection pixels, forming an image on a plurality of focus detection pixels by luminous fluxes of a target object that has passed through different pupil regions symmetrical relative to an optical axis of the imaging lens, and detecting a phase difference between the luminous fluxes of the target object.
It is known that the amount of luminous flux applied through the imaging lens decreases as the distance from the optical axis of the imaging lens becomes larger due to optical properties of the imaging lens in the imaging apparatuses. Accordingly, illuminance on the target object image formed on the image sensor exhibits non-uniformity. The process to correct non-uniformity of illuminance is called illuminance correction or shading correction. For example, the method for multiplying a correction coefficient in accordance with the distance from the optical axis by a pixel output is known as the illuminance correction. However, the method for multiplying a correction coefficient in accordance with the distance from the optical axis by a pixel output cannot be applied to a focus detection pixel since the amount of received light varies based on various conditions such as the arrangement of an opening. The imaging apparatus disclosed in Jpn. Pat. Appln. KOKAI Publication No. 2009-244858 includes a coefficient for focus detection pixels in addition to a correction coefficient for imaging pixels within a ROM provided to a camera main body, and selectively uses the corresponding correction coefficient for a pixel to be corrected.